Lubricating grease

ABSTRACT

LUBRICATING GREASES COMPRISING 5 TO 25% BY WEIGHT, BASED ON THE WEIGHT OF THE GREASES, OF THICKENING METAL SOAP, 1 TO 10% BY WEIGHT OF AN ANIONIC EMULSION OF UNOXIDIZE POLYETHYLENE HAVING A MEANS MOLECULAR WEIGHT HIGHER THAN 10,00 SAID EMULSION HAVING A POLYETHYLENE CONTENT RANGING FROM 35 TO 60% AND A METAL SULFINATE ANIONIC EMULSIFIER CONTENT RANGING FROM 8 TO 12% BASED ON THE WEGITH OF THE EMUSION, THE MEANS SIZE OF THE POLYETHYLENE PARTICLES BEING COMPRISED BETWEEN 0.02 AND 0.5 MICRON, THE REST OF THE COMPOSITION BEING AN OLEAGINOUS VEHICLE CONTAINING USUAL ADDITIVES FOR LUBRICATING GREASES.

United States Patent Int. 01. crom 5/22 US. Cl. 25233.2 5 Claims ABSTRACT OF THE DISCLOSURE Lubricating greases comprising 5 to 25% by weight, based on the weight of the greases, of thickening metal soap, 1 to by weight of an anionic emulsion of unoxidized polyethylene having a mean molecular weight higher than 10,000, said emulsion having a polyethylene content ranging from 35 to 60% and a metal sulfonate anionic emulsifier content ranging from 8 to 12% based on the weight of the emulsion, the means size of the polyethylene particles being comprised between 0.02 and 0.5 micron, the rest of the composition being an oleaginous vehicle containing usual additives for lubricating greases.

BACKGROUND OF THE INVENTION This invention relates to lubricating greases and more particularly to homogeneous greases with improved mechanical and chemical stability characteristics.

Heretofore, lubricating greases generally have been prepared from a lubricating base oil or oleaginous vehicle and a thickening agent which imparts the desired consistency to the grease. Thickening agents most often employed are soaps of fatty acids or inorganic components, such as colloidal silica, bentonite, and the like. The known greases are gels, the thickening agent forming a network wherein the oil is incorporated. However, difiiculties are encountered for manufacturing homogeneous and stable gels, due to many factors, such as type of thickening agent, type of base oil, the amounts of such components, the process for manufacturing the grease, etc.

The incorporation of polymers into lubricating greases to enhance some of their properties has resulted in further difiiculties. The use as thickening agents, of some olefin polymers, namely polyethylene and more particularly polyethylene having a density higher than 0.94 g./ cm. at 25 C., and copolymers of ethylene and propylene and propylene has been suggested. However, it has been observed that a slow oxidation and crystallization of these polymers occurs when the greases are subjected to friction stresses. Oxidized polyethylenes (with 0.2 to 7.5% by weight of chemically linked oxygen) have also been suggested and more particularly, complexes of these oxidized polyethylenes with a metal salt having a valency higher than 2 have been proposed. Greases containing these complexes are expensive and moreover they are not satisfactory for good lubricating performance. Generally, lubricating greases containing ethylene polymers are not sufiiciently stable and tend to break under mechanical stresses with formation of a too fluid product (U.S.'

3,809,649 Patented May 7,, 1974 A further object of this invention is to provide homogeneous and consistent lubricating greases.

SUMMARY OF THE INVENTION The present invention, which fulfills these and other objects is a lubricating grease comprising 5 to 25% by weight, based on the total weight of the grease, of thickening soap, 1 to 10% by weight of an anionic emulsion of unoxidized polyethylene having a mean molecular weight higher than 10,000, said emulsion having a polyethylene content ranging from 35 to 60% and an anionic emulsifier content ranging from 8 to 12% based on the weight of the emulsion, the mean size of the polyethylene particles being between 0.02 and 0.5 micron, and the rest of the lubricating grease being an oleaginous vehicle containing conventional additives for lubricating greases.

I It has been unexpectedly found that lubricating greases containing polyethylene emulsions as specified above, have noticeable consistency and are particularly stable under mechanical stresses.

DESCRIPTION OF PREFERRED EMBODIMENTS The polyethylene emulsions of the present invention are prepared according to processes described in US. Pats. 3,296,162 and 3,352,807. These emulsions are prepared by free-radical polymerization of ethylene in an aqueous medium containing a mixture of anionic emulsifying agents. The emulsions so obtained are then stabilized by a post-treatment which comprises covering substantially of the surface of the particles with an anionic emulsifying agent. With these stabilized polyethylene emulsions, the total content of emulsifying agent depends primarily upon the size of the polymer particles. For example, the content of emulsifying agent may be about 10% by weight when the particles contain 40% of solid material with a particle size of about 0.03 micron, whereas this content may be only 8% by weight when such particle size is about 0.5 micron. Generally, the content of emulsifying agent does not exceed 12% based on the weight of polymer emulsion, although higher contents could be used but without substantial improvement of the mechanical properties of the emulsions. The stabilizing post-treatment is carried out with anionic compounds which are free from acidic groups. The pH of the stabilized emulsions generally is higher than 8.

The stabilized polyethylene emulsions used in the present invention are quite different from the emulsions prepared from oxidized polyethylenes which generally have a relatively low molecular weight, usually lower than 5,000 and more often about 3,000. The molecular weight is in part set by the methods by which emulsions are prepared from the emulsifiable polyethylene solids. The mechanical properties of the polymers, however, generally depend upon their molecular weight. Moreover, the emulsions of oxidized polyethylenes normally do not contain more than 20 to 30% of solid materials. Accordingly, emulsions of unoxidized polyethylenes which are used in the lubricating greases of the present invention are quite different from the emulsions of oxidized polyethylenes, not only because of the higher content of polyethylene with a high molecular weight, higher than 10,000 and in the form of small particle sizes, but also because the pH of the unoxidized polyethylene is higher than 8 and gen erally, ranges between 8.5 and 10. Moreover, by contrast with the non stabilized emulsions of unoxidized polyethylenes, the polyethylene emulsions of the present in- 3 vention have an anionic emulsifying agent content of higher than 8%.

By incorporating stabilized emulsions of unoxidized polyethylene into mixtures of oleaginous vehicle and metallic soap, particularly consistent and smooth greases are obtained. This is believed due to a synergistic effect between the soap and the polyethylene emulsion. This improvement is obtained with other particularly suitable advantages, such as a better water resistance and a substantial reduction in the tendency to bleeding or oil separation.

The lubricating greases of the present invention most commonly employed generally contain from 1 to 10% by weight of stabilized emulsion of unoxidized polyethylene in admixture with to 25% by weight of soap, the rest of the grease being an oleaginous vehicle containing conventional additives for lubricating greases. A substantial improvement in the performance of the lubricating greases is obtained with a content in polyethylene emulsions as low as 1% by weight. In this connection, lubricating greases were prepared from naphthenic oil (SSU viscosity at 100 F.: 500) containing 8.5% by weight (based on the grease) of lithium 12-hydroxystearate, 0.5% of antioxydizing agent and 0.5 of rust-inhibiting agent. One of the greases (designated Grease A) was prepared without adding polyethylene emulsion, while other greases (designated Greases B, C and D) were prepared containing respectively 1%, 2% and 3% of stabilized anionic emulsion of unoxidized polyethylene (Poly-Em 12, a product of Cosden Oil & Chemical Company). The main characteristics of the polyethylene emulsion were:

The following tests were carried out on the greases:

Grease consistency by penetration test method ASTM D217: penetration is measured by the distance (in tenths millimeters) a standard cone will penetrate by free fall at 25 C. the surface of the grease placed in a cup. When the grease is merely placed in the cup, the penetration is reported as unworked. The unworked penetration of a grease being not always a suitable indication, the test is also carried out when the grease is worked in the worker cup (60 strokes in the present cast).

Water resistance test method ASTM D1264: the grease is water washed at controlled temperature and speed. The weight loss of grease is determined and calculated in weight pourcentage.

Bleeding test method IP number 121: the grease is subjected to a constant pressure and the amount of separated oil is determined (percent by weight). A

The specific composition and results of the tests on the four grease samples are given in the following table:

As noted above, the improvement in properties ofthe grease is substantial even with a content of polyethylene emulsion of 1% based on the total weight of the composition, and is particularly noticeable when the content is in the range of 2 to 3% by weight.

The amount of stabilized emulsion of unoxidized polyethylene which is employed to improve the properties of the greases may be varied depending on the type of oleaginous vehicle and on the type of and amount of soap. With emulsion contents higher than 10%, the improvement does not justify the additional expense of the added emulsion. Therefore, as a practical matter, the content of polyethylene emulsion generally does not exceed 10% and is most often employed in amounts of between about 1 and 5% by weight.

The oleaginous vehicle employed advantageously is an aromatic or naphthenic oil, more particularly, a highly naphthenic oil which leads to greases with a better thermal stability. Synthetic lubricating oils containing primarily sebacic or adipic esters of alcohols containing from 6 to 12 carbon atoms, such as 2-ethylhexanol, may be employed. However, mineral oils or mixtures of mineral oils and a lesser amount of synthetic oil are economically more advantageous.

The amount of soap used as thickening agent generally is between 5 and 25% of the Weight of the grease, this percentage depending on the type of soap, the amount of polyethylene, the desired degree of consistency, and like considerations. The soap employed may be virtually any of those commonly employed in lubricating greases. The soap preferably is one prepared from a higher aliphatic carboxylic acid, saturated or unsaturated, containing from 12 to 18 carbon atoms, such as stearic, 12-hydroxystearic, palmitic, oleic acids, and the like. Mixed soaps also may be used, these products being a mixture of two different soaps, such as a mixture of an alkaline soap and an aluminum soap. Other valuable thickening agents are complex soaps prepared from a higher aliphatic carboxylic acid and a low molecular weight acid, such as soaps of benzostearic, acetopalmitic or toluostearic acids.

The greases of the present invention also may include any of the usual additives, such as anti-oxidizing agents, rust-preventive agents and extreme-pressure additives. Particularly active anti-oxidizing agents are N-alkyl-paraphenylenediamines, naphthylamines and diand tri-alkylphenols. Rust-preventive agents useful include primary amines containing from 6 to 18 carbon atoms or N-heterocyclized derivatives. Extreme-pressure additives are generally selected from the group comprising arylphosphites, arylphosphates and arylthiophosphates, arylsulfides, sulfurized fatty oils, chlorinated parafiins, and the like. Antiwear additives, for example urea or thiourea derivatives, or some polyisobutylenes with a molecular weight higher than 800, acting as viscosity improvers, may also be added to the lubricating greases of the present invention. These additives may be employed in an amount which may vary between 0.1 and 10% by weight, more generally, between 1 and 5% based on the weight of the grease.

For preparing the lubricating greases of the present invention, known techniques may be used in carrying out the present process. Such process includes forming at a relatively high temperature, a homogeneous mixture of oleaginous vehicle and soap, adding the stabilized emulsion of polyethylene, cooling the mixture to form a gel and homogenizing this gel to obtain the desired structure. When preparing greases containing lithium 12-hydroxystearate, it may be convenient to slowly cool the homogeneous solution from a temperature of about 210 C. to a temperature of -130 C. and then to carry out an isothermal gelification at this temperature, the gel being then further cooled.

The following examples further illustrate the present invention but are not to be construed as limiting such invention. In these examples, the percentages are percentages by weight.

EXAMPLE 1 This example illustrates the synergistic effect between the soap and the emulsion of polyethylene.

A lubricating grease consisting of 85.5% by weight of naphthenic oil (500 SSU at 100 F.), 14% of sodium soap of stearic acid and 0.5% of anti-oxidizing agent was found to have a penetration (60 strokes) of 266.

Another grease consisting of 88% of the same oil, 10% of lithium stearate, 0.5% of the same anti-oxidizing agent and 1.5% of a polyethylene emulsion (Poly-Em 12) was found to have the same consistency.

These results show that by adding 1.5% of stabilized emulsion of unoxidized polyethylene, the amount of soap may be decreased from 14 to 10% without detrimental effect on the consistency of the grease.

On the th r hand, in preparing a lubricating grease from an oleag'nous vehicle and a stabilized emulsion of polyethylene, but without adding a metal soap, it was found that at least 10% by weight of emulsion was re quired to obtain a suitable consistency and even then, the grease was less stable.

EXAMPLE 2 A lubricating grease was prepared containing the following:

Percent Lithium 12-hydroxystearate 7.0 Anti-oxidizing agent 0.5 Rust-inhibiting agent 0.5 Mineral oil (500 SSU at 100 F.) 90.0 Polyethylene emulsion (Poly-Em 12) 2.0

This grease was homogeneous, smooth and hard. Moreover, its mechanical stability was good. From penetration tests, the difference between the penetration at 60 strokes and 10,000 strokes (respectively 276 and 285) was very small.

The loss by water washing was 4.5% by weight.

EXAMPLE 3 A lubricating grease was prepared containing the following:

Percent Lithium l2-hydroxystearate 6.5 Extreme-pressure additive 2.5 Naphthenic oil (2000 SSU at 100 F.) 35.0 Naphthenic oil (500 SSU at 100 F.) 53.0 Polyethylene emulsion (Poly-Em 12) 3.0

The grease of Example 3 was duplicated, but with the use of a mixed soap. This grease contained 5% by weight of lithium 12-hydroxystearate and 1.5% by weight of aluminum stearate.

The properties of this grease were the same as the properties of the grease of Example 3.

EXAMPLE 5 A lubricating grease was prepared containing the following:

Percent Calcium 12-hydroxystearate 7.5 Rust-inhibiting agent 1.0 Anti-oxidizing agent 0.5 Naphthenic oil (100 SSU at 100 F.) 86.5 Polyethylene emulsion (Poly-Em 12) 1.0

This grease has a penetration of 261 (at 60 strokes).

The water resistance of this grease is good, the loss by water washing (at 80 C.) being only 0.8% by weight.

By contrast, a similar grease containing the same amounts of soap, anti-oxidizing agent and rust-inhibiting additive and 87.5% of the same oil, but without polyethylene emulsion, had a penetration (at 60 strokes) of 295 and a loss by water washing of 18%. This comparative example shows the particularly favorable effect resulting from the addition of the stabilized emulsion of unoxidized polyethylene.

EXAMPLE 6 A lubricating grease was prepared containing the following:

Percent Calcium l2-hydroxystearate 5.0 Calcium acetopalmitate 5.0 Naphthenic oil (2000 SSU at 100 F.) 87.5 Polyethylene emulsion (Poly-Em 12) 1.0

This grease has a penetration (at 60 strokes) of 285 and a loss by water washing (at C.) of 1.4.

EXAMPLE 7 A lubricating grease was prepared containing the following:

Percent Sodium stearate 14.0 Anti-oxidizing agent 0.5 Naphthenic oil (500 SSU at F.) 45.5 Naphthenic oil (2000 SSU at 100 F.) 35.0 Polyethylene emulsion (Poly-Em 12) 5.0

This grease is particularly consistent, the penetration (at 60 strokes) being 207.

The loss by water washing (at 38 C.) is 40%, while a similar grease, but not containing polyethylene emulsion, shows a loss of 80% EXAMPLE 8 A lubricating grease was prepared containing the fol- This grease has a penetration (at 60 strokes) of 264.

These examples show that the lubricating greases of the present invention are consistent and mechanically stable, these improvements resulting from the incorporation in the lubricating greases of stabilized emulsions of unoxidized polyethylene as disclosed and discussed.

By way of comparison, a lubricating grease was prepared from 87.5% of mineral oil (500 SSU at 100 F.), 8.5% of lithium 12-hydroxystearate, 1% of usual additives and 3% of an unstabilized emulsion of polyethylene having a pH of 7.7 and a content of anionic emulsifying agent of 5.21%.

This grease had a penetration (at 60 strokes) of 312, a bleeding (or oil separation) index of 3.5 and a loss by water washing (at 80 C.) of 15%. By comparison with the results obtained with the Grease D of the table above presented, it is seen that unstabilized emulsions of polyethylene having a low content of anionic emulsifing agent, do not lead to a substantial improvement in the greases. Also, a grease similar with the above Grease D of the table, but prepared with the use of an emulsion of oxidized polyethylene was found to have poor mechanical stability, lumps being formed as a result of a breakdown of the emulsion and a coagulation of the polymer particles.

What is claimed is: 1

1. Lubricating greases comprising 5 to 25% by weight, based on the weight of the greases, of thickening metal soap; 1 to 10% by weight of an anionic emulsion of unoxidized polyethylene having a mean molecular weight higher than 10,000, said emulsion having a polyethylene content ranging from 35 to 60% and a metal sulfonate anionic emulsifier content ranging from 8 to 12% based 7 on the weight of the emulsion, the mean size of the polyethylene particles being comprised bet-ween 0.02 and ,0.5 micron, the rest of the composition being an oleaginous vehicle containing usual additives for lubricating greases.

2. The grease of claim 1 wherein the content of polyethylene emulsion is between'l and 5% by Weight.

3. The grease of claim 1 wherein the thickening soap is one prepared from a higher aliphatic carboxylic acid containing from 12 to 18 carbon atoms.

4. The grease of claim 3 wherein the thickening soap is one prepared from an acid selected from the group consisting of stearic, hydroxystearic, palmitic and oleicr 5. The grease of claim 1 wherein the pH of the anionic emulsion of unoxidized polyethylene is above 8.

8 References Cited UNITED STATES PATENTS 10/1957 Young et a1. 252-32 1/1970 Frye 252-59 DANIEL E. WYMAN, Primary Examiner I. VAUGHN, Assistant Examiner US. Cl. X.R. 

